Dafny vs Why3
Dafny
dafny.orgWhy3
why3.orgSide by side
| Figure | Dafny | Why3 |
|---|---|---|
| Price from | — | Free |
| Free plan | — | Yes |
| Free trial | — | — |
| Open source | — | — |
| Web | — | Yes |
| Windows | Yes | Yes |
| macOS | Yes | — |
| Linux | Yes | Yes |
| API | — | Yes |
| Self-hosted | Yes | Yes |
| Plans published | 0 | 1 |
| Spec score · Formal Verification Tools | 7.8 (#16) | 8.0 (#12) |
| License | The Dafny software is licensed under the MIT License. | TryWhy3 is distributed under the GNU Lesser General Public License version 2.1 with a special linking exception. |
| Purpose | It helps developers write code that can be verified against specifications to reduce the risk of late-stage bugs. | Why3 is a platform for deductive program verification that uses WhyML and external theorem provers to discharge verification conditions. |
| Support | The project homepage directs users to a Zulip channel to ask questions about Dafny. | The project provides a user mailing list, a Zulip chat, and a bug tracking system. |
Plans
In their own words
Why3
Why3 is a platform for deductive program verification. It uses WhyML to express programs and specifications, then works with external automated or interactive theorem provers to discharge verification conditions. WhyML supports preconditions, postconditions, assertions, and loop invariants, alongside logical theories and data structures such as arrays, queues, and hash tables. External provers need to be installed and configured separately. Why3 can be extended with support for new provers and used as a software library through its OCaml API. WhyML programs can be extracted automatically into correct-by-construction OCaml programs, and WhyML is also used as an intermediate language for verification of C, Java, Rust, and Ada. TryWhy3 provides a JavaScript version that runs in a browser. Installation options include Opam, Docker, source compilation, and listed Debian, Fedora, and Ubuntu packages. Its graphical interface saves proof attempts and transformations in an XML file and can replay obsolete attempts. Why3 is free and open source under GNU LGPL 2.1 with a special linking exception. Loop invariant inference is a work in progress, and many features remain very limited.